When you import media, Photoshop Elements stores the details of the imported files in a catalog. The catalog contains links to the files and records of details, such as tags that you attach to your media.
If you had created a catalog with a previous version of Photoshop Elements, Photoshop Elements prompts you to convert your catalog so that it is compatible with the current version. Converting a catalog is a one-time process. For more information, see Convert a catalog of a previous version.